Help Center/ Relational Database Service/ User Guide (Ankara Region)/ Working with RDS for MySQL/ Database Proxy (Read/Write Splitting)/ Rules for Distributing Weights
Updated on 2024-04-11 GMT+08:00
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Rules for Distributing Weights

This section describes the rules of distributing read weights to DB instances of different specifications.

Weight Distribution Rules

When the system automatically sets the read weights for DB instances, the weight values are fixed, as shown in the following table.

The default weight equals to the number of vCPUs multiplied by 50. The weight ranges from 100 to 1000.

Specifying Whether a SQL Statement Is Sent to the Primary DB Instance or Read Replica By Adding a Hint

Hints supported by RDS read/write splitting are as follows:

/*FORCE_MASTER*/: A SQL statement is executed on the primary DB instance.

/*FORCE_SLAVE*/: A SQL statement is executed on a read replica.

  • In addition to the weight distribution system of read/write splitting, hints are a useful type of SQL syntax that allows you to specify whether a SQL statement is executed on the primary DB instance or on a read replica.
  • Hints are only used as routing suggestions. In non-read-only SQL and non-transaction scenarios, SQL statements cannot be routed to read replicas.